Field of the Invention
The present invention relates to closed circuit coolers and evaporative refrigerant condensers.
Description of the Background
Both evaporative closed circuit coolers and evaporative refrigerant condensers utilize heat exchangers to transfer heat from an internal fluid or refrigerant indirectly to an external circulating fluid that is usually water. The circulating water, in turn, transfers heat and mass directly to the air. The air flow is induced or forced through the heat exchanger via a motive device such as a fan. The heat exchanger, in the established technology, consists of multiple serpentine tubes that are connected to the main fluid or refrigerant flow via header assemblies. The thermal capacity of these coolers and condensers is a function of the mass air flow rate as well as the internal and external heat transfer coefficients of the heat exchanger coil.
One previous technology advancement, over the original round bare tubes, improves the mass air flow rate by changing the round tube shape to elliptical, with the long axis of the ellipse parallel to the air flow direction (U.S. Pat. No. 4,755,331). Since the ellipse is more aerodynamically shaped than the round tube, the air flow resistance is reduced, air flow is subsequently increased, and, thereby, thermal capacity is increased.
Another previous technology improvement has changed the angles of the long axis of the ellipse in an alternating pattern, left and right. The thermal heat rejection capability of each tube increases with the canted pattern which also results in a larger spacing between tubes. This effectively reduces cost by reducing the number of tubes required to achieve the same heat rejection capability of the vertically positioned tube.
Another previous and significant technological advancement places spiral fins on the elliptical tubes of the heat exchanger at a specific spacing and fin height. This advancement increases the overall thermal capacity of the heat exchanger by a very significant amount. The fins are spaced along the length of the tubes so as to increase the thermal heat transfer coefficients without increasing the resistance to air flow. Since this technological advance also extends the total amount of heat transfer surface, it allows water conservation and visible plume reduction through partial or complete dry operation at reduced environmental air temperatures.